do i need to send proof of purchase
I'm unfortunately not sure why it wouldn't let you download the game. You can maybe try doing the download recovery via e-mail option here: https://itch.io/support
If that doesn't work, this sounds like something you'll need to contact itch.io support for directly as I can see that you purchased the game and should have access to it. I can confirm that other users are able to download the game from itch.io without issue.